An infiltration intake system including a structural body set in raw water is known in general, as disclosed in Japanese Patent Laying-Open No. 2013-75268, for example.
Japanese Patent Laying-Open No. 2013-75268 discloses an infiltration intake unit including a box-type housing set in seawater, a sand filtration layer stored in the housing, an intake pipe for supplying water passing through the sand filtration layer to a seawater desalination plant, a backwash pipe arranged above the sand filtration layer and a discharge pipe arranged above the sand filtration layer. The backwash pipe of this infiltration intake unit has a function of raising up foreign matter such as microorganisms and suspended substances accumulating on a surface layer of the sand filtration layer by injecting water or air. The discharge pipe has a function of injecting water for discharging the foreign matter raised up by the backwash pipe outward from the sand filtration layer.